The present invention relates to fuel cell interconnects, particularly to interconnects for fuel cell stacks, and more particular to flexible interconnects for fuel cell stacks which facilitates electrical connection and provides mechanical support with minimal mechanical stress.
Fuel cells are electrochemical devices that convert the chemical energy in fuels directly into electricity. Due to the thermodynamics of the reaction of the fuel and oxygen from air, single fuel cells have a voltage of about 1 volt. Thus, for practical applications, several cells must be stacked together to generate a higher voltage. The stacking of the cells require the use of an interconnect to electrically connect the cells. Most of the time, the interconnect also serves as the gas channels for the air and fuel flows. FIG. 1, described in detail herein after, shows an exploded view of a conventional fuel cell stack having a cross-flow design for the air and fuel.
In FIG. 1, the interconnect is made of an oxidation resistant alloy, and has spaced ribs that serve as the air and fuel channels. The structure is very similar to that of a heat exchanger. For good electrical contact, the interconnect must be in close physical contact with the single cells located on opposite sides. Due to the unavoidable slight curvature of the ceramic fuel cells, good contact over the entire cell difficult. In addition, the areas that are located below the ribs of the interconnect are not directly exposed to the gas and thus gas starvation could occur, leading to low stack efficiency. On the other had, interconnects with too thin ribs could have insufficient contact area with the cells. The stacking of metal interconnects with ceramic fuel cells can also cause high stress because of the rigidity of the structure and because of the difference in thermal behavior of metals and ceramics.
The present invention provides a solution to the above-reference problems associated with rigid ribs of the conventional interconnects, and provides in place of the rigid ribs, flexible xe2x80x9cfingersxe2x80x9d which will accommodate the imperfect flatness of the ceramic fuel cells. These flexible fingers enable improved electrical contact between cells and interconnects, and reduce the mechanical stress, as well as reducing areas subject to gas starvation.
It is an object of the present invention to provide fuel cell stacks with flexible interconnects.
A further object of the invention is to provide fuel cell interconnects that facilitates electrical connection and provides mechanical support with minimal mechanical stress.
Another object of the invention is to replace the rigid ribs of conventionally known fuel cell interconnects with interconnects having flexible fingers.
Another object of the invention is to provide fuel cell interconnections with flexible fingers which will accommodate any imperfect flatness of the fuel cells.
Another object of the invention is to provide interconnect plates having flexible fingers on both sides of the plate.
Another object of the invention is to provide interconnect plates wherein only the air side must be made of oxidation resistant material, and the fingers on the fuel side made of-flexible high conductivity material.
Another object of the invention is to provide back-to-back interconnect made from a single plate with fingers pointing up as well as down to form a common connection to two electrodes.
Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings. The present invention involves flexible interconnects for fuel cell stacks. The flexible member or fingers facilitates electrical connection, enables mechanical support with minimal mechanical stress, and the flexibility accommodates any imperfect flatness of the fuel cells, such as the ceramic cell. In addition, the area of the cell that is in contact with the fingers of the interconnect is smaller than the conventional rigid ribs and thus less gas starvation is provided. The interconnects can be made of three plates, for example, with a separator plate, a plate with flexible fingers or contact pads on the fuel side, and a plate with flexible fingers on the air side. Only the air side plate must be made of oxidation resistant material, while the fuel side plate can be made of flexible high conductivity material. Also, the interconnection can be fabrication in a back-to-back configuration from a single plate with flexible finger extending in opposite directions to form a common connection for two electrodes. The length and size of each flexible finger can be tailored to each individual application.